Lunar lander velocity before hitting ground

1. The problem statement, all variables and given/known data
A lunar lander is descending toward the moon's surface. Until the lander reaches the surface, its height above the surface of the moon is given by y(t)=b−ct+dt2, where b = 770m is the initial height of the lander above the surface, c = 62.0m/s , and d = 1.02m/s2 .
Part B: What is the velocity of the lunar lander before hitting the ground?

2. Relevant equations

3. The attempt at a solution
quadratic formula to find x intercepts. I don't know how I'm supposed to get the velocity before it hits the ground that could be at any point.